Rapid changes in flow rates in pipelines may produce rapid changes in pressures, or pressure surges, which travel along the pipeline often "snowballing" as they proceed. In some cases, the pressures exceed design pressure limits and must be reduced to avoid damaging the pipeline and creating a serious safety hazard as well as damaging the environment.
One obvious method of relieving such pressure surges is by the installation of fixed pressure relief valve devices. However, such devices are efficient only if situated at a point in the pipeline where the design pressure limits are exceeded. Otherwise, an attempt to anticipate a surge by setting the device to open at a fixed high pressure, which may be indicative of a building surge, though not in and of itself dangerous, could result in unnecessarily relieving high pressure occurences resulting from normal pressure fluctuations. A more reliable parameter is the rate of pressure change and some existing surge relief systems are designed to unload a quantity of fluid from the pipeline to a reservoir in the event that pressure in the pipeline increases at an inordinate rate. However, such systems are dependent upon the operating parameters of the pipeline, and each system must be designed for the particular pipeline in which it is to be installed.